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Formation of 70S ribosomes: large activation energy is required for the adaptation of exclusively the small ribosomal subunit

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http://pubman.mpdl.mpg.de/cone/persons/resource/persons50104

Blaha,  Gregor
Ribosomes, Max Planck Institute for Molecular Genetics, Max Planck Society;

Burkhardt,  Nils
Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons50444

Nierhaus,  Knud H.
Ribosomes, Max Planck Institute for Molecular Genetics, Max Planck Society;

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Blaha, G., Burkhardt, N., & Nierhaus, K. H. (2002). Formation of 70S ribosomes: large activation energy is required for the adaptation of exclusively the small ribosomal subunit. Biophysical Chemistry, 96(2-3), 153-161.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0010-8C5A-1
Abstract
Association of ribosomal subunits is an essential reaction during the initiation phase of protein synthesis. Optimal conditions for 70S formation in vitro were determined to 20 mM Mg2+ and 30 mM K+. Under these conditions, the association reaction proceeds with first order kinetics, suggesting a conformational change to be the rate-limiting step. 70S formation separates into two sub-reactions, the adaptation of the ribosomal subunits to the association conditions and the association step itself. The activation energy of the process was determined to 78 kJ/mol and revealed to be required exclusively for the adaptation of the small subunit, rather than the large subunit or the association step. The presence of mRNA [poly(U)] together with cognate AcPhe-tRNA, accelerates the association rate significantly, forming a well-defined 70S peak in sucrose gradient profiles. mRNA alone provokes an equivalent acceleration, however, the resulting 70S couple impresses as an ill-defined, broad peak, probably indicating the readiness of the ribosome for tRNA binding, upon which the ribosome flips into a defined state.